Inflammation and immune activation are associated with risk of Mycobacterium tuberculosis infection in BCG-vaccinated infants

Tuberculosis vaccine development is hindered by the lack of validated immune correlates of protection. Exploring immune correlates of risk of disease and/or infection in prospective samples can inform this field. We investigate whether previously identified immune correlates of risk of TB disease also associate with increased risk of M.tb infection in BCG-vaccinated South African infants, who became infected with M.tb during 2-3 years of follow-up. M.tb infection is defined by conversion to positive reactivity in the QuantiFERON test. We demonstrate that inflammation and immune activation are associated with risk of M.tb infection. Ag85A-specific IgG is elevated in infants that were subsequently infected with M.tb , and this is coupled with upregulated gene expression of immunoglobulin-associated genes and type-I interferon. Plasma levels of IFN- α 2, TNF- α , CXCL10 (IP-10) and complement C2 are also higher in infants that were subsequently infected with M.tb .